Ship propulsion with a gondola-like synchronous motor

ABSTRACT

To improve the propulsion efficiency of a ship propulsion having a housing to be arranged on the bottom of the hull in a gondola-like manner, with a synchronous motor in the housing, at propulsion powers of approximately 10 MW, the rotor of the synchronous motor is designed as a permanent-magnet rotor, and the stator of the synchronous motor is fitted into the housing in a form-fitting manner to be cooled through the housing wall. An additional cooling device in the form of a fan or a spray device may be provided for each winding overhang.

FIELD OF THE INVENTION

The present invention relates to ship propulsion and may be applied inthe design of a synchronous motor which is located in a hydrodynamicallydesigned part of a housing arranged on the bottom of the ship's hull forthe purpose of directly driving a propeller.

BACKGROUND INFORMATION

In conventional ship propulsion, described in U.S. Pat. No. 2,714,866, amotor is provided which is a three-phase alternating current motor witha squirrel-cage rotor, with the rotor sitting on a hollow shaft which isin turn linked to the drive shaft running inside the hollow shaft by acoupling. The drive shaft is coupled directly to the propeller. In thisship propulsion system, the stator of the motor is surrounded by atubular housing which is in turn inserted into a pipe hanger-typehousing part mounted gondola fashion on the bottom of the hull. Themotor including the rotor bearings is cooled with fresh water pumpedfrom a tank arranged in the hull into the interior of the motor housingand circulated throughout. (see, e.g., U.S. Pat. No. 2,714,866).

German Patent No. 917 475 describes a ship propulsion of a silimilardesign, the stator of the three-phase motor is fitted into thehydrodynamically designed housing part in a form-fitting manner to coolit by water flowing past this housing part. The interior of the housingpart accommodating the three-phase motor is filled with water underpressure. This water is provided for bearing lubrication and heattransfer.

In another convention ship propulsion described in U.S. Pat. No.5,403,216 and a publication “A New Generation of Standard Diesel ElecticRoRo Ferry” by Kvaerner Masa Yard, which may be designed for a drivepower of 10 MW or more, the dynamoelectric motor is supported with itsstator on radially arranged web plates in the surrounding housing; theweb plates used in this manner serve at the same time to form coolingchannels for a gaseous coolant supplied from the marine hull. Asynchronous motor with a squirrel-cage rotor is usually used as themotor, with the rotor optionally cooled by its arrangement on the hollowdrive shaft through which water flows. With such a propulsion device,the ratio between the maximum diameter of the drive housing and thepropeller diameter are selected so that the ratio between the two isless than 0.65, preferably in the range between 0.4 and 0.5. It shouldbe recalled here that the propeller diameter cannot be selected of anydesired size. The above-mentioned ratio of outside diameters influencesthe propulsion efficiency, which is inversely proportional to, theabove-mentioned diameter ratio.

To cool an electric motor operated underwater, it is also known thatinsulation oil used as coolant can be pumped in circulation so that itreleases heat to the surrounding water in cooling channels runningaxially in the area of the housing wall (U.S. Pat. No. 2,862,122 A). Itis also known that high power (1 to 2 MW) three-phase motors set upoutdoors can be cooled by passing a stream of air produced by a fanalong the wall of the housing (German journal Siemens-Z. 1966, no. 40,page 13 ff.).

SUMMARY

An object of the present invention is to provide a system propulsionsystem with a drive power in the MW range while guaranteeing a favorablepropulsion efficiency.

This object is achieved according to the present invention by the factthat three-phase motor is a synchronous motor and has a drive power ofat least 2 MW, the rotor of the synchronous motor is a permanent-magnetrotor, and the interior of the housing parts accommodating thesynchronous motor is free of flowing coolant.

With such a design of the propulsion device, no additional coolingmeasures need to be taken to cool the drive motor because of the use ofa synchronous motor with a permanent-magnet rotor that producespractically no heat losses due to current. In addition, since apermanent-magnet rotor is smaller radially than a squirrel-cage rotor,the radial space required by the drive motor is reduced. This leads to amore advantageous ratio between the outside diameter of the drivehousing and the outside diameter of the propeller, so that thepropulsion system has an excellent propulsion efficiency for a shippropulsion of this magnitude. In particular, when taking the measuresaccording to the present invention, it is possible to design shippropulsions where the ratio of the outside diameter of thehydrodynamically designed housing part to the outside diameter of thepropeller is less than or at most equal to 0.4.

Permanent-magnet rotors may be used instead of squirrel cage rotors orrotors separately energized via collector rings with synchronous motors,in particular for electric machines with drive powers up to about 30 kW(see, e.g., Siemens-Z. 1975, no. 49, pp. 368-374). Such motors withdrive powers of about 2 to 5 MW have already been designed for submarinepropeller drives, with the axially very short motor, which is thusrelatively large with respect to its outside diameter, being arrangedinside the hull. With this motor the pole shoes of the rotor arecomposed of several permanent magnets made of a special samarium-cobaltalloy and are glued to the pole shaft. The stator core assembly of thismotor is surrounded by two cooling rings through which fresh waterflows. The fresh water is recooled by seawater in heat exchangers (see,e.g., brochure PERMASYN-Motoren für U-Boot-Propellerantriebe by SiemensA G, order No. E 10 001-A930-A29, and “Yearbook of the ShipbuildingSociety”, 1987, pp. 221-227).

If a ship propulsion designed according to the present invention is usedin the upper power range (more than 5 to 10 MW), effective cooling ofthe winding overhang is important. It may then be expedient to providean additional cooling device for each winding overhang of the stator.These additional cooling devices may be arranged in the interior space,which is present anyway due to the motor design, without any particularadditional expense. Either fans arranged on the rotor shaft inside thewinding overhang or a ring with a tubular cross section for each windinghead at the end, this ring being provided with spray holes and itsinterior being connected by a pump to an insulating oil sump below therotor shaft, may be used as cooling devices. In both variants, heat isremoved from the coolant, whether air or insulating oil, in the same wayas heat is removed from the stator via the surrounding motor housingwall.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a longitudinal section of a propulsion device withair cooling of the winding overhangs of the stator according to anembodiment of the present invention.

FIG. 2 illustrates a longitudinal section of a propulsion device withspray cooling of the winding overhangs according to an embodiment of thepresent invention.

DETAILED DESCRIPTION

The propulsion device according to FIG. 1 has a hydrodynamicallydesigned housing part 1 in the form of a gondola with a synchronousmotor arranged in it, the synchronous motor having a stator 7 and arotor 10, and a shaft 20, with the help of which the propulsion devicemay be mounted on the bottom of a hull in the manner of a gondola.Housing part 1 has hollow cylindrical part 2 and end caps 3 and 4, whichcarry the bearings of drive shaft 5. Propeller 6 is arranged on one endof the drive shaft 5.

Stator 7 of the synchronous motor is fitted in a form-fitting mannerinto the hollow cylindrical part 2, with this part of housing 1 beingshrunk-fit onto the stator core assembly, for example. The windings ofthe stator are visible in winding overhangs 8 and 9. Rotor 10 of thesynchronous motor is designed in a conventional manner as apermanent-magnet rotor, resting on drive shaft 5 with a supportingstructure 11. Supporting structure 11 has axial passages 16.

A fan 12 is provided on drive shaft 5 inside each winding overhang 8 and9. With the help of this fan, air in the interior of the synchronousmotor is stirred up and flows past winding overhangs 8 and 9. Thesynchronous motor as a whole is cooled essentially through hollowcylindrical part 2 of housing 1, releasing heat to the water flowingpast it with the movement of the ship.

In the embodiment according to FIG. 2, a ring 13 with a tubular crosssection is arranged on each end of the winding overhangs 8 and 9 to coolthese winding overhangs and is provided with spray orifices 15 in thedirection of the winding overhangs. Insulating oil in sump 14 belowdrive shaft 5 may be sprayed through these spray orifices, being pumpedfrom the sump into ring 13 by a pump located outside housing part 1.Heat is also removed from insulating oil sump 14 through housing part 1,as is also from the air stirred up according to FIG. 1. Sump 14 shouldnot include the air gap of the motor. Spray rings 13 may be provided inaddition to or as an alternative to fans 12.

Due to the fact that the synchronous generator with its stator isinserted in a form-fitting manner into hydrodynamically designed housingpart 1, and permanent-magnet rotor 10 takes up less space radially thanwould a squirrel-cage rotor, housing part 1 may have a relatively smalloutside diameter d, so the ratio of outside diameter d of housing part 1to outside diameter D of propeller 6 achieves a relatively small valueof 0.35, for example, even if the synchronous motor is designed for adrive power of 2 to 20 MW or more.

This design of the new propulsion device does not depend on whether thegondola is mounted rigidly or rotatably on the hull. Thus, it is alsosuitable for bulkhead drives.

What is claimed is:
 1. An electric propulsion device for a ship,comprising: a gondola type housing mounted on a bottom of a hull of theship, the gondola type housing having a hydrodynamically designedhousing part, the hydrodynamically designed housing part having aninterior free of a streaming coolant coming from outside of thehydrodynamically designed housing part; and a three-phase synchronousmotor accommodated in the hydrodynamically designed housing part, thethree-phase synchronous motor having a propulsion power of at least 2MW, a permanent-magnet rotor, a rotor shaft attached to at least onepropeller, and a stator, the stator being fitted into thehydrodynamically designed housing part in a form-fitting manner andbeing cooled by water flowing past the hydrodynamically designed housingpart, an outside diameter of the hydrodynamically designed housing partbeing at most 40% of an outside diameter of the at least one propeller.2. The electric propulsion device according to claim 1, furthercomprising winding overhangs associated with the stator and anadditional cooling device for each winding overhang.
 3. The electricpropulsion device according to claim 2, wherein the additional coolingdevice includes a fan arranged on the rotor shaft inside each respectivewinding overhang for stirring up air in the interior of the synchronousmotor.
 4. The electric propulsion device according to claim 2, furthercomprising: a ring having spray holes on an end for each windingoverhang of the stator, an interior of the ring being coupled by a pumpto an insulation oil sump below the rotor shaft for spraying oil ontothe winding overhangs.
 5. The electric propulsion device according toclaim 1, wherein the hydrodynamically designed housing part includes ahollow cylindrical part, the hollow cylindrical part being shrunk-fitonto a stator core assembly.